Abstract: To characterize the long terminal repeat (LTR) of different subgroups of ALVs,fragments of 5' LTR of subgroup J strains HN06 and NX0101,subgroup A isolate GD08 and subgroup B isolate CD08 were cloned and subjected to sequence analysis. The 5' LTRs of HN06 and NX0101 had an 90.8% to 97.5% nucleotide sequence identity in comparison with other ALV-J strains. The 5'LTR of GD08 had the highest identity of 94.6％ with that of the domestic strain SDAU09C1 of ALV-A and had a lower nucleotide sequence identity of 91.7％ and 92.4％ with HN06 and NX0101,respectively. The nucleotide sequence of CD08 5'LTR was highly identified with that of ALV-J 5'LTRs. The R region had a high nucleotide similarity,while the U3 and U5 regions showed variance. To compare the promoter activities,the 5'LTR fragments of different ALV isolates were inserted into the pCAT-basic vector and transfected into DF-1 cells,respectively. Kinetic analysis for CAT activity showed that the promoter activities of 5'LTR from HN06 and NX0101 were similar,as well as that form GD08 and CD08. While there were significant differences in activity between ALV-J and GD08 or CD08.

Key words: avian leukosis viruses of different subgroups; 5'LTR; promoter activity